Monitoring fastening loading

ABSTRACT

A retrofit system for providing a load indicator on a foundation bolt. The system includes a fastener having a fastener head, gauge length and central fastener bore in the gauge length and head. A datum rod is anchored in the central bore with a free datum rod being moveable longitudinally relative to the fastener head during elongation of the fastener gauge length. An internally threaded fastener portion below the central fastener bore is configured to thread over a foundation bolt. A compression sleeve positioned over the foundation bolt is configured to receive the load indicating fastener therein and to bear the compressive forces of the fastening. Elongation of the gauge length as the fastener is tightened onto the stud is manifest as displacement of the datum rod end, which displacement is measured to provide an indication of fastener loading.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims the benefit of U.S. ProvisionalApplication No. 61/175,683, filed May 5, 2009, which is incorporatedherein in its entirety by reference.

BACKGROUND

1. Field of the Invention

This invention relates to monitoring loads in fastenings, and moreparticularly to in-fastening load monitors.

2. Description of the Related Art

Fasteners are used in a wide variety of industrial installations whereachieving proper fastener loading (tension) and maintaining this loadingin service can be problematic. Monitoring the load on a fastener duringinstallation and service can be equally problematic.

Many industrial fastening applications require a predetermined loadingat installation and periodic monitoring of loading to ensure thatloading remains within an acceptable range. Checking the loading with atorque wrench typically requires loosening and then retorquing of thefastening. This is particularly onerous in high corrosion and high cycleloading applications.

Overtightening a fastener can lead to catastrophic failures. Conversely,fasteners typically experience some loss of tension in service due to,for example, a variety of in-service occurrences including: relaxation(thread embedment), vibration loosening, compressive deformation in thejoint or flange, temperature expansion or contraction, etc. Loss oftension from these occurrences can cause misalignment or premature wearin a bolted assembly, leakage (in applications where the fastener isused for sealing), or catastrophic joint failure due to excessively highloads on other members of the assembly.

In certain applications, knowledge of a fastener load, upon installationand over time, is desirable for avoiding the potentially dangerousconsequences of a compromised or loosened fastener, such as slippage,wear, leakage and/or possible failure. In other applications, forexample when working with a group of bolts around a flange of a sealedassembly, it is important to evenly tighten the group of bolts. Byuniformly tightening a group of bolts or studs to an appropriate load,and maintaining this load over time, potential failures are less likelyto be experienced.

Accordingly, improvements are sought in determining and monitoringfastener loading.

SUMMARY

It has been discovered that existing foundation bolt installations maybe retrofit with a load indicator for in-use load monitoring. A hardenedgauge nut is used to cut the foundation bolt to a predetermined length.The gauge nut is then removed and a load indicating assembly isinstalled on the foundation bolt. A centering plate and compressionsleeve are placed over the foundation bolt. The centering plate has anannular rim for centering the compression sleeve. A fastener having afastener head, gauge length, central bore and internally threadedportion is threaded onto the foundation bolt within the sleeve. A splitwasher can be assembled around the gauge length portion of the fastenerbetween the fastener head and compression sleeve. The split washer caninclude a collar which is received within the sleeve and is partiallyretained in the sleeve.

One aspect of the invention features a load indicating fastening systemfor use in a fastening. The system includes a fastener having a fastenerhead and a fastener gauge length below the head. The head and gaugelength together define a central fastener bore. A datum rod has alongitudinal length with a first end anchored at a first portion of thecentral bore and a substantially free datum end closer to the fastenerhead and moveable longitudinally relative to the fastener head duringelongation of the fastener gauge length. An internally threaded fastenerportion below the central fastener bore is configured to thread overexternal threads of a complementary stud, such as foundation bolt. Acompression sleeve is sized to receive the internally threaded fastenerportion and the fastener gauge length and to bear the compression forcesof the fastening between the fastened head and the fastening jointsurface. A base washer can be used between the compression sleeve andthe joint surface. The base washer can include a rim or other featurefor centering or otherwise positioning or retaining the compressionsleeve.

In some cases, the stud is a foundation bolt. In some cases, the stud isthe threaded portion of a bolt. In some cases, the stud is a thread rodsuch as thread stock.

In some implementations, the compression sleeve is constructed withsufficient column strength to be substantially incompressible undernormal fastening loading, e.g., below the yield load of the foundationbolt.

In some implementations, the system further includes a split washerbetween the fastener head and the top of the compression sleeve. In somecases, a portion of the split washer is positioned radially between thegauge length and the compression sleeve. For example, in some cases, thesplit washer includes a shoulder or collar configured to fit within thecompression sleeve to substantially align the split washer and gaugelength within the compression sleeve. The collar on the split washer isreceived in the compression sleeve interior to retain the split washer.

In some cases, the compression sleeve is substantially cylindrical.Preferably, the compression sleeve is constructed to substantiallyresist deformation during elongation of the fastener gauge length. Thisensures that the measured load accurately reflects gauge lengthelongation.

In some implementations, the system further includes a lever pivotallyfixed within the central bore of the gauge length and responsive todisplacement of the datum rod within the central bore. The leverprovides an amplified response to the displacement. In some cases, thesystem further includes a second lever pivotally fixed within thecentral bore and responsive to the first lever. In some cases, thefastener gauge length is of a lesser outer diameter than the outerdiameter of the internally threaded fastener portion.

In some implementations, the system further includes a base washer witha semi-spherical projection and a complementary seat on the compressionsleeve to allow for variable alignment of the compression sleeve on thespherical projection of the washer. In some cases, the compressionsleeve defines a hemi-spherical seat to receive hemi-sphericalprojection of the centering base over a range of angles. The range ofmovement between the projection and seat accommodates a wide range ofdifferences between the anchor bolt and flange angle. In some cases, aninternal diameter of the compression sleeve serves as a seat for thehemi-spherical projection of the centering base washer. In someimplementations, the base washer includes a shoulder configured to alignthe compression sleeve with the washer.

In some implementations, the fastener head defines a datum referencesurface configured such that displacement of the datum end is measurablerelative to the datum reference surface to determine loading.

In some implementations, the system further includes a datum rod enddisplacement reader. The reader measures and amplifies a change in thegauge length base on datum rod displacement. The reader or “indicator”can be fixed within or removably coupled to the fastener. In some cases,the indicator is disposed within the bore above the datum rod. In othercases, the indicator is positioned atop the fastener head above thedatum rod. Thus, integral or removable readers may be used in variousimplementations.

Another aspect of the invention features a method of measuring a loadapplied to a fastening. The method includes sizing the length of one ofa compression sleeve and an externally threaded stud to provide apredetermined length of compression sleeve beyond an end of the stud ina fastening to be formed. The method further includes positioning acompression sleeve over an externally threaded stud and positioning aportion of a fastener within the compression sleeve. The fastenerincludes a fastener head and a fastener gauge length below the head. Thehead and gauge length together define a central fastener bore. A datumrod has a longitudinal length with a first end anchored at a firstportion of the central bore and a substantially free datum end closer tothe fastener head and moveable longitudinally relative to the fastenerhead during elongation of the fastener gauge length. An internallythreaded fastener portion below the central fastener bore is configuredto thread over external threads of a complementary stud. A compressionsleeve is sized to receive the internally threaded fastener portion andthe fastener gauge length. The method further includes threading theinternally threaded fastener portion onto the externally threaded stud,tightening the fastener onto the stud to apply a compressive force tothe compression sleeve, and measuring displacement of the datum rod todetermine fastener elongation and thereby the loading in the fastening.

In some applications, the method further includes positioning a washeror spacer between the fastener head and the compression sleeve. In somecases, the washer is a split washer. The split washer centers thefastener within the compression sleeve and provides a bearing surfacefor the fastener head.

In some applications, measuring displacement of the gauge length isperformed by non-contact methods, e.g., by measuring a property of a gapformed between the datum rod end and a reference surface on the fastenerhead. For example, properties can be measured by sonic, resistive,optical or other techniques know in the art.

In some applications, the load indicating system can be installed on aselected number of fasteners in a machinery foundation, such as a windturbine foundation or industrial compressor foundation. An electronicreader, such as the SPC4™ reader available from Valley Forge and BoltManufacturing Co., can be used to remotely monitor elongation andthereby the loading of the selected fastenings. Alternatively, fixed orremovable mechanical or in-bore readers, such as those used in theMaxbolt™ bolts or dual lever readers available from Valley Forge andBolt Manufacturing Co. can be used, for in-person monitoring. Thus, thesystem can provide statistical assurance that the foundation fasteningsare sufficiently tight. This is particularly important, in installationexperiencing high frequency reciprocating forces such as those presentin wind turbines, mills, and other industrial installations.

In some applications, the system may be an original installation. Insome applications, the system is installed as a retrofit to existingfoundation installations. The internally threaded portion is threaded onto the existing stud within the compression sleeve after cutting thestud to a predetermined length. A hardened gauge nut or other suitablegauge can be used to aid in trimming the nut and to clean the threadsupon removal.

The fastener is then tightened, compressing the sleeve between the headof the fastener and the foundation adjacent the foundation stud. Theinstantaneous loading can readily determined at a glance using a visualscale on an elongation reader. The reader can be temporarily mounted onthe fastener or can be fixed within the central bore of the fastener.

The fastener and sleeve can be sized for any number of applications. Insome applications, it is advantageous for the sleeve and fastener to beas short as possible. Accordingly, the stud is trimmed to apredetermined length and the sleeve and fastener are sized to providemeasurable elongation of the gauge length as determined by measuringdisplacement of the datum rod within the central bore. The fastenergauge length can be necked down to obtain a shortened gauge length forshortened assemblies.

Thus, the fastener loads can be measured to determine whether loadingsare within an acceptable window or range, e.g., 40-60 percent window ofacceptability, of operational loading. For example, a reading more thanplus or minus 10 percent outside a predetermined operating range can besignal a need for retightening or replacing a fastener.

In some implementations, a mechanical reader or “indicator” contacts thedatum rod. In some cases a first and/or second lever are pivotallyconnected within a reader housing and responsive to datum roddisplacement. The levers cooperate such that a load display pointer orother indicator is responsive to movement of the first and/or secondlevers.

In some implementations, the load indicator provides an electricalsignal, an audible signal or a visual signal.

In some external indicator implementations, coupler interfaces on thefastener and the indicator couple the indicator to the fastener via atleast one of a snap fit, interference fit, threaded fit, and magneticattraction. In some cases, the interfaces are configured to align thedatum probe with the free end of the datum rod.

An example indicator includes a housing defining a fastener interfaceconfigured to removably couple the housing to a fastener. A moveabledatum probe extends from the housing. The fastener interface isconfigured to align the datum probe with a datum rod of a fastener. Afirst lever is pivotally mounted within the housing and is moveable inresponse to displacement of the datum probe. A load display isconfigured to indicate a degree of loading of a fastener as a functionof displacement of the datum probe. In some cases, the load displayincludes a visual scale and a pointer associated with the first lever.

In some implementations, a second lever is associated with the firstlever to produce a second amplified response to movement of the datumprobe.

In some implementations, the fastener head defines a reference surfaceand a load indicator indexing interface. A free end of the datum rodmoves relative to a reference surface on the fastener head upon loadingand elongation of the fastener. In some cases, a portion of thereference surface also serves as the load indicator indexing surface.The load indicator indexing interface on the fastener head and the boltindexing interface on the load indicator provides for alignment and/ortemporary mounting of the load indicator atop the fastener.

As the load indicator is pressed onto the bolt head, the datum probe ofthe load indicator is progressively pushed into the load indicatorhousing until the bolt indexing interface engages the load indicatorindexing interface. Displacement of the free end of the datum rodrelative to the reference surface is translated into a measurement offastener loading via the corresponding movement of the datum probe,levers and pointer. Thus, the pointer moves along the visual scale ofthe load indicator in proportion to the displacement of the datum probe,e.g., by measuring a corresponding gap produced between the referencesurface and datum rod as a result of fastener loading. In some cases,the gap between the datum rod and reference surface can be additionallyor alternatively measured using sonic, optical, or resistancemeasurements or other non-contact gap measuring techniques.

In some implementations, a load indicator includes first and secondcooperating levers, each having first and second ends. The first freeend of the first lever serves as the datum probe and the second free endof the second lever serves as the pointer. The levers are pivotallyretained on pivot pins within the load indicator housing. A spring orother biasing device serves to bias one or more of the levers in aparticular direction. For example, in some cases, a spring biases thecooperating levers such that the pointer rests adjacent the 100% portionof the visual scale. As the load indicator is mounted on the fastener,the datum probe contacts the datum rod and moves the pointer down thevisual scale to the appropriate percentile load indicator. In somecases, the use of multiple levers provides for amplified pointerresponse while allowing the load indicator housing to be of a compactconstruction. In some cases, the load indicator can fit entirely withinthe central bore.

In some implementations, the load indicator is configured to be furtherconnected to a power tightening tool to facilitate automatic shut-off ofthe tool upon reaching a certain loading, as signaled by the loadindicator. For example, the load indicator can provide an electricalsignal corresponding to the movement of the datum probe and the tool canbe configured to shut-off upon detection of a predetermined electricalsignal value. In a particular case, the load indicator is positionedwithin a driver on the tool such that the load indicator and driver aresimultaneously pressed onto the fastener.

In some implementations, the load indicator can be coupled to a fastenerto provide ongoing loading measurements. For example, the load indicatorcan be snap fit or interference fit onto a fastener head for periodicreadings or can be threaded onto the fastener head or otherwise fixedlymounted to provide ongoing measurements. Thus, the load indicator can beremovably or effectively permanently attached to the fastener to providea desired frequency of readings. In some cases the indicator includes asensor for sensing said displacement of the datum probe and translatingthe displacement into a readable signal. In some cases, the sensorincludes one of a displacement transducer and a pressure transducer.

In some implementations, multiple levers within the load indicator maycooperate to indicate the load on the fastener by amplification of theelongation experienced by the fastener. A multi-lever design may be usedto provide a visible range of pointer movement even with a significantlyreduced indicator diameter and a reduced indicator depth. Use of twolevers in a load indicator reduces the range of movement and the degreeof clearance required for the first lever. For in-fastenerimplementations, this significantly reduces the dimensions of thesection of the fastener bore required to accommodate the amplified leverresponse. Additional advantages afforded by the present inventioninclude increased sensitivity of the load indicator, a reduction in theoverall length of load indicator and in the depth of the bore.

In some implementations, a load indicator can be incorporated into thefastener itself. For example, a cartridge carrying the two levers may bepress-fitted or threaded into the central bore. Various implementationsmay include a seal between the cartridge and fastener to protect theload indicator from water, chemicals, dirt, and other environmentalconditions.

In some implementations, a load indicator may be removably coupled to afastener with a displacement gauge precisely indexed relative to thefastener head via a plurality of indexing projections on the loadindicator that engage a coupler on the fastener head. The precisepositioning or “indexing” of the displacement gauge relative to areference surface defined on the male coupler of the fastener headallows for precise measurement of fastener elongation based on movementof a datum rod disposed in a bore in the fastener.

A load indicator can be removably coupled to a male coupler on afastener via a and includes a gauge housing defining a female couplerhaving an interior dimension sized to receive at least a portion of themale coupler defined on the fastener head. A displacement gauge isdisposed within the housing and includes a moveable probe disposedwithin the female coupler and engageable response to movement of thesecond free end of the datum rod when the load indicator is coupled tothe fastener. A plurality of indexing projections are spaced about aninterior of the female coupler and moveable to engage the male couplerof the fastener head to thereby index the moveable probe relative to thefastener proximate to the second free end of the datum rod. In somecases, the male coupler includes discreet recess. In some cases, themale coupler includes an annular recess for receiving the projections.

The details of one or more implementations of the invention are setforth in the accompanying drawings and the description below. Otherfeatures, objects, and advantages of the invention will be apparent fromthe description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features, and advantages made apparent to those skilled in theart by referencing the accompanying drawings.

FIG. 1 is an exploded perspective view of a load indicating fasteningsystem.

FIG. 2 is a perspective side view of a fastening including the loadindicating fastening system of FIG. 1.

FIG. 3 is a cross-sectional view of the internally threaded fastener andsplit washer of FIGS. 1-2.

FIG. 4 is an exploded perspective view of another load indicatingfastening system including an in-fastener indicator.

FIG. 5 is a schematic diagram of a central bore of a fastener housing asingle-lever in-fastener load indicating assembly.

FIG. 6 is a schematic diagram of a central bore of a fastener housing adual-lever in-fastener load indicating assembly, under an applied load.

FIG. 7 is a schematic diagram of the central fastener bore and loadindicating assembly of FIG. 6 without a load.

FIGS. 8A-8B are schematic diagrams of a cartridge for retaining thelevers of an in-fastener load indicating assembly.

FIG. 9 is a cross-sectional view of an internally threaded fastener andsplit washer showing the datum rod anchored within the central bore anda coupler for a removable indicator.

FIG. 10 is a perspective view of a removable load indicator for use withthe fastener of FIG. 9.

FIG. 11 is a cross-sectional view of the load indicator of FIG. 10.

FIG. 12 is a side view of the load indicator of FIG. 10 coupled to thefastener of FIG. 7.

FIG. 13 is a cross-sectional view of the load indicator of FIG. 10.

FIG. 14 is a side view of the load indicator of FIG. 10 coupled to thefastener of FIG. 7.

Like reference symbols in the various drawings indicate like elements.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

With reference to FIG. 1, a load indicating fastening system 101 formspart of a fastening. System 101 includes a fastener 102 having afastener head 104, a fastener gauge length 106 below head 104. Head 104and gauge length 106 together define a central fastener bore 108.

A datum rod 110 has a longitudinal length with a first end anchored at afirst portion of the central bore 108 and a substantially free datum endcloser to the fastener head 104 and moveable longitudinally relative tothe fastener head 104 during elongation of the fastener gauge length106.

An internally threaded fastener portion 112 extends below the centralfastener bore 108 and gauge length 106. Internally threaded fastenerportion 112 is configured to thread over external threads of acomplementary stud 109, such as a foundation bolt. A compression sleeve114 is sized to receive the internally threaded fastener portion 112 andthe fastener gauge length 106.

A split washer 116 is provided between fastener 102 and compressionsleeve 114. In some cases, split washer 116 is between fastener head 104and a top surface of compression sleeve 114. In some cases, a portion ofthe split washer is disposed in an annular space between gauge length106 and interior surface of compression sleeve 114. For example, splitwasher 116 can include a collar or shoulder configured to be receivedwithin the compression sleeve to aid in aligning or centering fastener102 within compression 116. Split washer 116 provides a bearing orcontact surface under fastener head 104 other than the top surface ofcompression sleeve 114.

An annular centering base 118 is first placed over stud 109 on a fixedfastening surface 111, such as a foundation plate or pipeline flange.Centering base 118 is configured with a rim 120 sized to receivecompression sleeve 114 to center compression sleeve 114 relative to stud109.

In other implementations, the centering base includes a hemi-sphericalcentral projection for improved centering or alignment of compressionsleeve 114 on stud 109 extending from an inclined fastening surface 111.For example, stud 109 may extend at an acute angle to surface 111 insome applications. A lower end of compression sleeve 114 can bepositioned over the hemi-spherical projection on centering base 118 andadjusted to substantially align compression sleeve 114 about stud 109 topermit threading of portion 112 onto stud 109. Thus, centering base 118may be configured to accommodate various angles of stud 109 relative tosurface 111. In some cases, centering base 118 may be tapered tocompensate for a complementary angle between stud 109 and surface 111.

In some implementations, centering base 118 and compression sleeve 114can include additional complementary features. For example, anti-shearor counter-force features can be used to prevent rotation of compressionsleeve 114. Such features can include a slotted ring to provide areaction point for a reaction bar.

With reference to FIG. 2, a fastening is made including the loadindicating fastening system 101 of FIG. 1. The system 101 is used tomeasure a load applied to the fastening.

During installation of system 101, a gauge nut is threaded onto stud109, which is then cut to a predetermined length with reference to thenut. The nut further serves to clear or reform the threads at thesevered end of stud 109. Alternatively, compression sleeve 114 can besized to cooperate with any given stud length to provided a knowncombination of stud length and sleeve length. As can be appreciated, thepredetermined stud and sleeve lengths provide a known reference forsystem 101 relative to base surface 108.

Centering base 118 is then placed over stud 109 with rim 120 facing up.Compression sleeve 114 is then positioned within rim 120 over stud 109.In cases in which a hemi-spherical projection is provided on centeringbase 118, compression sleeve 114 is adjusted on the projection tosubstantially align compression sleeve 114 longitudinally with stud 109.

The two halves of split washer 116 are then assembled together aroundgauge length 106 of fastener 102. Internally threaded portion 112 andgauge length 106 of fastener 102 are then inserted, together with acollar portion of split washer 116 into compression sleeve 114. Fastenerhead 104 is then driven to threadably engage internally threaded portion112 and stud 109. Fastener head 104 is further driven to tightenfastener 102 onto stud 109 to apply a compressive force to compressionsleeve 114. Upon loading, elongation of gauge length 106 is measured todetermine loading of the fastening.

With reference to FIG. 3, a cross-sectional view of fastener 102illustrates operation of datum rod 110 within central bore 108 offastener 102. A first end 122 of datum rod 110 is anchored with a lowerportion of central bore 108 to provide a fixed reference at one lowerportion of gauge length 106. Datum rod 110 extends along central bore108 to a free datum rod end 124 adjacent fastener head 104.

Fastener head 104 is provided with a reference surface 126 having aknown unloaded position relative to free datum rod end 124. For example,datum rod end 124 is depicted here as being a fixed distance from a topsurface 126 of fastener head 104. In some cases, datum rod end 124 issubstantially coplanar with a reference surface 126, e.g., top surface,of fastener head 104 in an unloaded state.

As fastener head 104 is driven to tighten fastener 102 and compresssleeve 114, gauge length 106 ultimately exhibits a measurableelongation. Gauge length elongation, and thereby loading, is determinedby measuring displacement of the datum rod free end 124 relative toreference surface 126 to determine the loading in the fastening.

In some implementations, datum rod free end 124 is positioned below anin-bore integrated datum rod reader as disclosed in U.S. Pat. No.5,668,323 issued Sep. 16, 1997 to Cory S. Waxman, and U.S. Pat. No.7,520,174, issued Apr. 21, 2009 to Applicant, which are included hereinby reference in their entirety.

Thus, aspects of the invention can be used in different implementationswith external and in-bore or in-fastener datum rod displacementindicators. In particular implementations, external or in-bore readerscan be used to provide electrical signals to control operation of a tooldriving fastener head 104.

With reference to FIG. 4, system 101 a includes a fastener 102 a havingan in-bore indicator 128 positioned within central bore 108 formed infastener head 104 and gauge length 106. In-bore indicator 128 caninclude one or more levers as previously described

In some implementations, an optional reaction ring interlocks with ahole in the compression sleeve and provides a reaction point duringtightening or loosening of fastener 102. The reaction ring can beslipped over the compression sleeve and a spring loaded pin snaps intothe hole in the sleeve to prevent the sleeve from turning. The reactionring defines slots for receiving a reaction bar. The hole is formed nearthe top of the sleeve to prevent twisting of the sleeve.

In some implementations, a load indicator includes a housing or“cartridge” housing connecting various indicator elements. The housingor cartridge may be temporarily mounted to the head of a fastener or maybe permanently mounted within a fastener bore to measure the tensileload of the fastener. The cartridge includes moveable members, e.g.,levers or dials, that interact to provide an amplified response to theelongation of the fastener to provide a visual indication along a visualscale.

With reference to FIG. 5, a schematic diagram shows a cut-away view ofan in-fastener single lever load indicator 1 within an elongatedinternal bore 4 of a fastener, including bore sections 4 a, 4 b, and 4 cextending from the head of the fastener to a lower internal point. Boresection 4 a extends into the gauge length of the fastener and isconfigured to receive a reference datum rod 6 configured to act upon asingle elongated lever 8 disposed in bore section 4 b. Lever 8 ismoveable within bore 4 about a pivot 10 in response to movement of datumrod 6 during elongation of the fastener. The dashed lines indicate theresting position 5 of lever 8 prior to elongation of the fastener andthe corresponding solid lines indicate the elongation position 7 oflever 8. As a first end 12 of lever 8 moves in contact with datum rod 6a second end 14 of lever 8 produces an amplified response, moving secondend 14 between position 5 and position 7. Section 4 c is configured toaccommodate the amplified range of movement of second end 14. Thus, asmaller, less visible movement of datum rod 6 within bore 4 is convertedinto a larger, more visible movement at second end 14 of lever 8.

With the single lever configuration shown in FIG. 5, the depth anddiameter of bore section 4 c is determined by the desired amplifiedrange of movement of second end 14 and the length of lever 8. Forexample, for the range of movement of second end 14 to travel a fullhalf inch visual scale, the diameter of section 4 c must besubstantially equal to one half inch. The depth of section 4 c, in turn,must be sufficient to provide clearance for movement of the remaininglength of lever 8. Single lever indicators have proven very reliable andeffective but have typically been limited to use in fasteners havinglarger shanks or thicker heads due to the required depth of bore section4 c. Thus, use of multiple levers provides for a significantly shallowerbore section 4 c to enable use of load indicator 1 in fasteners havingsmaller diameter shanks and smaller heads.

With reference to FIG. 6, a cut-away view is shown of a load indicator 1having a first lever 8 within bore section 4 b and a second lever 16disposed within bore section 4 c. First end 12 of lever 8 engages datumrod 6 disposed in bore section 4 a causing lever 8 to respond tomovement of datum rod 6 during elongation of the fastener. Datum rod 6may be integral to the fastener or may be a separate component insertedinto bore section 4.

A datum rod 6 comprises a post 7 configured to extend a predetermineddistance into section 4 a in the shank of the fastener. Differentlengths of post 7 may be used to enable use of a standard size of loadindicator 1 with various lengths of fasteners having various lengths ofbore 4. Datum rod 6 further includes an annular rim 9 about the top ofpost 7. Pivot 10 and any portion of lever 8 may extend into the openingin the center of annular rim 9. Annular rim 9 serves to contact firstend 12 of lever 8 independent of the orientation of load indicator 1within bore 4. It is understood that datum rod 6 may include any othersuitable feature for engaging lever 8 and may be configured for aparticular orientation of load indicator 1 within bore 4. Datum rod 6may anchored at its lower end in section 4 a and substantially freealong the length of post 7 to convey elongation of bore 4 to loadindicator 1.

With continued reference to FIG. 6, a second lever 16 is disposed withinbore 4 and is moveable about second pivot 18. A first end 20 of secondlever 16 is responsive to movement of second end 14 of lever 8 causingcorresponding movement of a second end 22 of second lever 16. First end20 may be configured to engage lever 8 in both directions.Alternatively, second lever 16 may be biased in one direction andmoveable in a second direction in response to movement of lever 8.

Second lever 16 may be sized and configured to provide any desireddegree of response to movement of lever 1. For example, second pivot 18may be positioned at the midpoint of second lever 16 or may be shiftedtowards one end to further amplify the response of second lever 16. Forexample, both levers 8 and 16 may produce amplified responses, with thesum response being significantly greater than that provided by a singlelever of comparable length. Second lever 16 is depicted with secondpivot 18 positioned adjacent first end 20 of second lever 16 to providean amplified response at second end 22 of second lever 16. Bore section4 c is sized to accommodate the amplified response movement of secondlever 16.

Comparison of FIGS. 5 and 6 demonstrates on advantage provided by use ofmultiple levers with in-fastener mounting regarding the depth of boresection 4 c. By limiting the range of movement of lever 8 to the smallerdiameter of bore section 4 b and shifting the broader amplified responseto second lever 16, the degree of clearance required for lever 8 issignificantly reduced and the depth of section 4 c is likewisesignificantly reduced. Additional advantages afforded by aspects of thepresent invention include increased sensitivity of load indicator 1, areduction in the overall length of load indicator 1 and in the depth ofbore 4. Further advantages included increased manufacturing efficiency,less loss of fastener material to bore 4, and compatibility with smalleror more conventional fasteners. A multi-lever configuration providessimilar advantages in separable indicators. For example, the indicatorhousing or cartridge may be made more compact for use in tighter areasor with smaller fasteners while allowing for use of wrenches or othertools to tighten the fastener.

With reference to FIG. 7, a schematic diagram of a cut-away view of theload indicator of FIG. 6 is shown with levers 8 and 16 in a secondposition corresponding to maximum elongation of the fastener as well asto the default position of levers 8 and 16 prior to insertion into bore4. During installation and calibration of load indicator 1 in bore 4 ofa fastener, datum rod 6 is first installed in bore section 4 a and loadindicator 1 is then press-fitted or threaded into bore 4 or is otherwisesecured to the fastener. Additional methods of attaching load indicator1 to a fastener are described with reference to FIGS. 5-6.

Load indicator 1 is advanced within bore 4 until first end 12 of lever 8contacts datum rod 6. Load indicator 1 is further advanced until thesecond end 22 of second lever 16 indicates zero load on a visual scaleassociated with second lever 16. It is understood that any number ofload indicator components may be suitably independently or jointlyinstalled and adjusted to achieve calibration of load indicator 1. Asdatum rod 6 moves due to elongation of the fastener, second end 22 ofsecond lever 16 travels along the visual scale to indicate thecorresponding elongation or loading conditions.

In an alternative implementation, load indicator 1 may include or beattached to an electronic circuit or other mechanism for initiating autoshut-off of a pneumatic tightening tool or other powered tool to preventover-tightening. Load indicator 1 can also be attached electronically toa remote reader for automated monitoring of the clamp load status of alarge number of fasteners 2.

With reference now to FIGS. 8A-8B, a schematic diagram of a cut-awayview of a load indicator installed within fastener 2. In oneimplementation, load indicator 1 includes cartridge 36 configured forinsertion into bore 4. Cartridge 36 retains pivots 10 and 18 securinglevers 8 and 16 within bore 4. Cartridge 36 may further retain a springfor biasing one of levers 8 or 16 in a default position. Association oflevers 8 and 16 and pivots 10 and 18 with cartridge 36 facilitates easyinstallation and removal of load indicator 1 from bore 4. Cartridge 36is connected at its upper end to bezel 28. Cartridge 36 can be recessedwithin the fastener head or may be mounted on top of the fastener.

With reference now to FIG. 9, a fastener 2 is configured for use with aseparable tensile load indicator shown in FIGS. 10-12. Fastener 2defines a central bore 4 extending from the head 3 of fastener 2 intothe gauge length of the fastener. Datum rod 6 is anchored at a lower end6 a within bore 4. Head 3 of fastener 2 further defines a load indicatorinterface 5 for use as a reference surface and/or for use in aligningand/or temporarily mounting or coupling a load indicator on fastener 2.Top reference surface 5 a of load indicator interface 5 and topreference surface 6 b of datum rod 6 are coplanar when fastener 2 is ina non-loaded state. As fastener 2 is tightened, bore 4 is elongateddrawing datum rod top surface 6 b downward away from top surface 5 a ofload indicator interface 5. In other implementations the datum rod andreference surface are not necessarily coplanar and another predeterminedunloaded relative positioning of the free end of the datum rod and thereference surface can be used.

With reference to FIG. 13, a load indicator 200 is shown coupled to afastener 202. Load indicator 200 includes a gauge housing 204 and adisplacement gauge 206 disposed within housing 204. Gauge housing 204includes a female coupler 208 at one end for coupling to a complementarymale coupler formed on the head of fastener 202.

With reference to FIG. 14, load indicator 200 is indexed and removablycoupled to fastener 202 via a male coupler 210 defined on fastener 202.Displacement gauge 206 is disposed within housing 204 and includes aprobe 214 disposed within female coupler 208. A plurality of indexingprojections 222 are spaced about an interior of female coupler 208 andare moveable to engage male coupler 210 to index probe 214 relative tofastener 202.

A datum rod 212 is anchored at a first end within a central bore 213defined in fastener 202 such that elongation of fastener 202 causesdisplacement of a second free end of datum rod 212 relative to malecoupler 210. Displacement of datum rod 212 is measured by probe 214 toprovide an indication of fastener loading.

Female coupler 208 includes a piston 218 bearing probe 214. Piston 218is biased towards an unlocked or decoupled position via spring 228.Spring 228 may be a coil spring concentric to piston 218 and actingbetween housing 204 and a flange or other feature formed on piston 218.

A sleeve 220 is positioned concentric to piston 218 and bears aplurality of indexing projections 222. Indexing projections are shown asball bearings retained in a journal formed radially through sleeve 220.A locking ring 224 is positioned concentric to sleeve 220 and is biasedby coil spring 226 towards a locked position in which locking ring 224maintains indexing projections 222 in engagement with indexing contour216 on male coupler 210. Piston 218 is retractable within sleeve 220 viainsertion of male coupler 210. Indexing projections 222 are inwardlyextendable in response to movement of locking ring 224 into the lockedposition to thereby engage indexing contour 216 on male coupler 210 andsecurely index probe 214 relative to fastener 202.

Spring loading of piston 218 and locking ring 224 provide for snap-fitindexing and coupling of loading indicator 200 to fastener 202 bysliding female coupler 208 over male coupler 210. For example, femalecoupler 208 is pressed onto male coupler 210 until an end face of piston218, which forms a seat portion of female coupler 208, contacts and endface of male coupler 210. Continued movement of female coupler 208 overmale coupler 210 compresses spring 228 as male coupler 210 displacespiston 218 within sleeve 220. As the indexing contour 216 on malecoupler 210 aligns with indexing projections 222, indexing projections222 are urged into engagement with indexing contour 216 by spring loadedlocking ring 224.

Indexing projections 222 are shown as ball locks, e.g., ball bearingsformed of stainless steel. In alternative implementations, indexingprojections may include non-spherical elements such as spring tabsdepending from sleeve 220 or other feature suitable to engage anindexing contour 216 formed on male coupler 210.

Indexing contour 216 is shown as a circumferential groove or annularrecess defined on a lateral surface of male coupler 210. Indexingcontour 216 allows indexing projections 222 to engage male coupler 210at any rotational orientation of load indicator 200 atop fastener 202.The semi-circular profile of and circumferential continuity of indexingcontour 216 provides a self-centering alignment aspect of indexing ofload indicator 200 atop fastener 202.

“Indexing” as used herein refers to precise positioning of probe 214relative to a fixed reference on fastener 202, e.g., an end face of malecoupler 210. This precise positioning can include both axial and radialalignment and positioning components. For example, probe 212 can beindexed to fastener 202 via indexing projections 222 to both positionthe probe 212 axially proximate or in abutment with datum rod 212 andradially centered over datum rod 212. Accordingly, indexing contour 216on male coupler 210 and indexing projections 222 on load indicator 200cooperate to index probe 214 relative to a fixed reference surface offastener 202, such as an end face of male coupler 210. Displacement of afree end of datum rod 212 relative to the end face of male coupler 210or other fixed reference surface can provide an indication of fastenerelongation and thereby loading in fastener 202.

In some implementations, the end face of male coupler 210 or other fixedreference surface can be used in combination with indexing projections222 in and indexing contour 216 to securely index probe 214. Thus, insome cases, indexing projections 222 may be the primary or even solemeans of indexing probe 214, while in some cases, additional couplerfeatures may additionally contribute to indexing of probe 214.

In some implementations, displacement gauge 206 is moveable withinhousing 204 with movement of piston 218. Movement of probe 214 relativeto piston 218 and the connected displacement gauge 206 provides anindication of displacement of datum rod 212 and elongation of fastener202. In some cases, probe 214 includes at its tip a ball bearing toprovide a point contact with the free end of datum rod 212. The ballbearing is axially movable within an axial journal to act upon a pushrod causing a dial of a dial gauge to traverse a dial gauge scalevisible through an opening defined in housing 204. It will beappreciated that a common dial gauge or any other suitable mechanical,electro-mechanical, or electrical gauge or probe may be used inconjunction with the described indexing features to obtain a suitablyprecise measurement of elongation and lending.

Housing 204, piston 218, sleeve 220 and locking ring 224 may bemachined, molded or otherwise formed of aluminum, steel, brass, or othersuitably durable and rigid material, e.g., plastic or compositematerial. Locking ring 224 can include a taper, knurling, or otherfeature to facilitate retraction of locking ring 224 to decouple loadindicator 200 from fastener 202. Retraction of locking ring 224 moves alocking portion of locking ring 224 out of locking engagement withindexing projections 222. Upon retraction of locking ring 224, indexingprojections may be retracted from engagement with indexing contour 216of male coupler 210 and load indicator 200 may be decoupled fromfastener 202.

A number of implementations of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, internally threaded portion 12 can be configured as a femalecoupling for receiving stud 9 and a male threaded extension of gaugelength 6. Accordingly, other implementations are within the scope of thefollowing claims.

1. A load indicating fastening system for use in a fastening, the systemcomprising: a fastener comprising: a fastener head; a fastener gaugelength below the head and defining, together with the head a centralfastener bore; a datum rod having a longitudinal length with a first endanchored at a first portion of the central bore and a substantially freedatum end extending toward the fastener head and moveable longitudinallyrelative to the fastener head during elongation of the fastener gaugelength; and an internally threaded fastener portion below the centralfastener bore and configured to thread over external threads of acomplementary stud; and a compression sleeve sized to receive theinternally threaded fastener portion and the fastener gauge length andconfigured to bear a compressive force of the fastening.
 2. The systemof claim 1, wherein the compression sleeve is constructed withsufficient column strength to be a substantially incompressible undernormal fastening loading.
 3. The system of claim 1, further comprising asplit washer between the fastener head and the compression sleeve. 4.The system of claim 3, wherein the split washer includes a shoulderconfigured to fit within the compression sleeve to substantially alignthe gauge length longitudinally within the compression sleeve.
 5. Thesystem of claim 1, further comprising a male coupling feature defined onthe fastener head for removably coupling a load indicator thereto. 6.The system of claim 5, further comprising the load indicator, whereinthe load indicator comprises a plurality of indexing projections spacedabout an interior of a female coupler portion of the load indicator, theindexing projections being moveable to engage the male coupler of thefastener head to thereby index the load indicator relative to the malecoupler of the fastener head for measurement of displacement of the freeend of the datum rod.
 7. The system of claim 1, further comprising alever pivotally fixed within the central bore and responsive todisplacement of the datum rod within the central bore.
 8. The system ofclaim 1, further comprising a second lever pivotally fixed within thecentral bore and responsive to the first lever.
 9. The system of claim1, further comprising a base washer between the compression sleeve and ajoint surface.
 10. The system of claim 1, further comprising asemi-spherical base washer and a complementary seat on the compressionsleeve to allow for variable angular alignment of the compression sleeveon the spherical washer.
 11. The system of claim 1, wherein the fastenerhead defines a datum reference surface configured such that displacementof the free datum rod end is measurable relative to the referencesurface to determine loading.
 12. The system of claim 11, furthercomprising a free datum rod end displacement reader.
 13. The system ofclaim 1, further comprising a base washer including a rim configured toalign the compression sleeve with the base washer about the stud. 14.The system of claim 1, wherein the fastener gauge length is of a lesserouter diameter than the outer diameter of the internally threadedfastener portion.
 15. The system of claim 1, wherein the compressionsleeve further comprises a counter-torque reaction feature for useduring tightening of the fastener.
 16. A method of retrofitting afoundation bolt installation with a load indicator, the methodcomprising: cutting the foundation bolt to a predetermined length;installing a compression sleeve over the foundation bolt; threading afastener onto the foundation bolt within the sleeve, the fastener havinga fastener head, gauge length and internally threaded portion; andwherein the fastener further includes a central bore and a datum rodanchored within the central bore to provide an indication of elongationof the gauge length.
 17. The method claim 16, further comprising using ahardened gauge nut to measure where to cut the foundation bolt to apredetermined length.
 18. The method of claim 16, further comprisingmeasuring displacement of the free datum rod end relative to a referencesurface to determine the loading of the fastener and foundation bolt.19. A method of measuring a load applied to a fastening, the methodcomprising: selecting the length of one of a compression sleeve and anexternally threaded stud to provide a predetermined length ofcompression sleeve beyond an end of the stud in a fastening to beformed; positioning the compression sleeve over an externally threadedstud; positioning a portion of a fastener within the compression sleeve,the fastener comprising: a fastener head; a fastener gauge length belowthe head; and an internally threaded fastener portion below the centralfastener bore and configured to thread over external threads of theexternally threaded stud; threading the internally threaded fastenerportion onto the externally threaded stud; tightening the fastener ontothe stud to apply a compressive force to the compression sleeve; andmeasuring elongation of the fastener to determine the loading in thefastening.
 20. The method of claim 19, wherein measuring elongation isperformed by measuring displacement of a datum rode anchored within abore in the gauge length relative to the fastener head.